1. Field of the Invention
The present invention relates to an optical disk writing method and a device for writing information by forming written marks having physical properties different from those of the other portions on a recording medium.
2. Description of the Related Art
As writable type optical disks, many kinds of disks such as a CD-R/RW, a DVD-RAM, a DVD±R/RW and a Blu-ray Disc (BD) have been commercialized and widely used. As one of major technologies of increasing a capacity of an optical disk in the future, there is a multilayer technology of forming a plurality of recording layers. As examples of the multilayer technology, DVD±R and BD-RE dual-layer disks have been already commercialized. In a writing type optical disk device, a write power of each medium is calibrated depending on variable factors, such as a temperature, a wavelength of a light source and variations in manufacturing of a medium, by use of a method called Optimum Power Calibration (OPC), in order to constantly write user data with a proper write power.
As to a multilayer disk, in order to prevent occurrence of an error in determination of the write power due to return light from layers other than a layer in which the OPC is executed (hereinafter the return light is called inter-layer interference), devices are generally adopted for currently manufactured dual-layer disks. For example, OPC execution regions of respective layers are laid out not to overlap with each other in the thickness direction. As the OPC method, the following methods are known.    (1) OPC Method Mainly for Write-Once DiskAs an example of an OPC method using asymmetry, Japanese Patent Application Laid-Open Official Gazette No. Hei 6 (1994)-139574 discloses an OPC technology using a method of equalizing asymmetry of a repetitive signal of a shortest mark and a space and asymmetry of a repetitive signal of a longest mark and a space.    (2) OPC Method Mainly for Rewritable DiskAs an example of an OPC method using signal modulation depth (or reflectance), Japanese Patent Application Laid-Open Official Gazette No. 2000-306241 discloses an OPC technology using a method of finding a write power by multiplying a power, which maximizes a change in the reflectance relative to a change in the write power, by a coefficient. Moreover, Japanese Patent Application Laid-Open Official Gazette No. 2003-067925 discloses an OPC technology using a method of determining a write power by use of a slope itself of a change in a modulation depth relative to the write power or a slope of a change in a γ value. Here, the γ value is a value standardized by use of a rate of the change in the modulation depth and a rate of a change in the write power, and is an indicator robust to a set offset of the write power. As the same kind of indicator, there is a so-called κ value. By use of the κ value, a threshold power of writing can be accurately obtained. Since the so-called γ value and κ value are widely known among optical disk engineers and are beyond the scope of the present invention, detailed description thereof will not be given here.    (3) OPC Method Mainly for Sector Format Disk
Japanese Patent Application Laid-Open Official Gazette No. Hei 10 (1998)-320777 discloses an OPC technology using a method for determining a write power based on an amount equivalent to jitter which is measured by measuring a phase difference between a PLL clock and a data edge.